iio: adc: rzg2l_adc: Prepare for the addition of RZ/G3S support

iio: adc: rzg2l_adc: Prepare for the addition of RZ/G3S support

The ADC IP available on the RZ/G3S differs slightly from the one found on
the RZ/G2L. The identified differences are as follows:
- different number of channels (one being used for temperature conversion);
  consequently, various registers differ
- different default sampling periods
- the RZ/G3S variant lacks the ADVIC register.

To accommodate these differences, the rzg2l_adc driver has been updated by
introducing the struct rzg2l_adc_hw_params, which encapsulates the
hardware-specific differences between the IP variants. A pointer to an
object of type struct rzg2l_adc_hw_params is embedded in
struct rzg2l_adc_data.

Additionally, the completion member of struct rzg2l_adc_data was relocated
to avoid potential padding, if any.

The code has been adjusted to utilize hardware-specific parameters stored
in the new structure instead of relying on plain macros.

The check of chan->channel in rzg2l_adc_read_raw() function, against the
driver specific mask was removed as the subsystem should have already
been done this before reaching the rzg2l_adc_read_raw() function. Along
with it the local variable ch was dropped as chan->channel could be used
instead.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://patch.msgid.link/20241206111337.726244-10-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>